Basics of Observing and Timing Grazing Occultations presented 2014 July 12, UMD Obs., College Park, MD 32 nd Annual IOTA Meeting David W. Dunham

Lunar Occultation Geometry

Lunar profile projected onto Earth’s surface during grazing occultation

Free IOTA Observer’s Manual available at For visual timings, use For mobile and video use, WWV short-wave time signals give the cheapest accurate time base. 5.0 & 10.0 megahertz at night and 15.0 megahertz for day use.

This is the 2 nd page (page 370) of the 2-page article about the 1963 October 8 th zeta Tauri graze in S&T’s Dec issue

The 1964 publication of Watts’ charts gave us the possibility to predict the lunar profile for grazing occultations This was published in the 1964 Feb. issue of Sky and Telescope. The figure at the bottom for WA  was in the range for a graze we observed that month, so I knew from it that a high mountain would dominate our profile.

1970 July 11, standing on the Milwaukee cable trailer at our wedding in Highland Park, Illinois From left to right, Tom Van Flandern, Ronald Abileah, Homer DaBoll, Edward Halbach, David Dunham, and Joan Dunham

Finally, I observed a graze of  2 Capricorni with 12 others near Ruther Glen, VA on 1977 June 5, Moon 83%-, CA 3N, Sun alt. -2  In spite of the conditions, the events were easily seen with the star’s 3.1-mag. brilliance. In the meantime, the International Occultation Timing Association (IOTA) had been formally established as a dues-paying organization in July 1975, primarily to promote the observation and analysis of lunar grazing occultations. _____

Lunar Profile from Graze of delta Cancri – 1981 May 9-10 Alan Fiala, USNO, obtained the first video recording of multiple events during this graze, with 7 D’s and 7 R’s Circled dots are Watts’ predicted limb corrections

Video of 1990 April Aldebaran Grazing Occultation from Poland Graze Observer’s Handbook available for $21 from Hal Povenmire, – also, research on tektites

The First Multiple Stations were Deployed for Grazing Occultations In the 1990’s, I often thought, the equipment is doing all the work, maybe I should be somewhere else making another observation. For a graze of omicron Leonis the morning of 1998 November 12, I set up a 5-in. clock-driven SCT at Delta, Pennsylvania, near York I left a student there after showing him how to make adjustments to keep the star in the field of view, and set up another telescope about 0.5 km away to record the event When I came back, he was excited to see the multiple occultations of the star. “Did you make any adjustments?” “No”. “At least, you were there to protect the equipment”. “Actually, it was the other way around. Whenever a car drove by, I hid behind the telescope box.”

2001 Dec. 21 Grazing Occultation of 4.0-mag.  2 Aqr Moon 32%+, Cusp Angle 12S Observed from 8 stations at Kitty Hawk, North Carolina, by only 4 observers. Kitty Hawk has many summer homes, unoccupied on a December weekday, so we had many safe places to set up telescopes 1 to 2 hours before the graze. 4 of the video stations were unattended Also observed from 6 stations in Georgia

My Telescopes for Remote Observation

Mighty Midi – Orion 80mm short tube Can record occultations of stars to mag. 11.0, even mag under good conditions; these work better for grazes I use visual finder scope and $60 Quantanray tripod while scotty uses a mighty mini video as the finder and MX-350 tripod (not as sturdy as the Quantanray)

Eta Geminorum - Graze Grazing Occultation of 3.5-mag. eta Geminorum in Arizona, 2011 April 10, my first success with remote mini/midi stations (a humiliating defeat, it was machines, 3; humans, 0) Moon 36%+ Cusp Angle 15N

Stations on N. 387 th Ave. N. Remote Cen. Remote S. Remote Attended

Comparison of Kaguya & LRO profiles Here is a recent reduction of observations of the 2011 April 10 th eta Geminorum graze by Dr. Mitsuru Sôma at the Japanese National Observatory. The profiles are close, but LRO’s, with more orbits and points than Kaguya, is more accurate near Axis Angles 14.3 and With multiple stations and LRO data, there are still new things that can be done with grazing occultations!

Graze of 4.9-mag.  2 Tauri (ZC 628) over Minneapolis, Minn. on 2012 Aug. 11, Moon 35%-, CA 2N Produced with Occult 4 & at I made plans to observe it from near Grant. With the small cusp angle, I thought that there would be too much glare to record with midi systems, but I took 2 of them, to try, and 2 4-inch SCT’s for attended stations that Joan and I ran. But like in Arizona, the machines triumphed; it was machines, 2, humans, 0. Station 3 recorded 6 D’s and 6 R’s; I’ll play the video. __ Station 4’s single R indicates a south shift of about 200m; we can still determine corrections to stellar proper motions from graze observations Google map to plot graze paths & find observing sites

Kaguya profile for graze of 6.2-mag. ZC  from north cusp of 17% sunlit waning Moon

Locations of our 3 stations for the August 2 nd graze of ZC 798 in the dark parking lot of Hanover High School, west of US 301 about 15 miles n.e. of Richmond, VA